class String
def hello
"world"
end
end
String.class_eval {
def world
"hello"
end
}
"a".world
=> "hello"
"b".hello
=> "world"
解决方法
通过class_eval,您可以做更多动态的事情：
>> met = "hello" #=> "hello"
>> String.class_eval "def #{met} ; 'hello' ; end" #=> nil
>> "foo".hello #=> "hello"